One section of this program deals with genetic control of capsid morphogenesis in bacteriophage T4. We have studied mutations which bring about the presence of many particles with abnormally shaped heads. Precise genetic mapping has shown that these until now fall into gene 23 (length variants) and gene 22 (length and diameter variations). Within gene 23 there is some evidence that morphogenetic mutations are clustered in three short segments of that gene, suggesting that certain parts of the protein have special form-controlling genes to obtain additional evidence regarding clustering, and in the hope of implicating other genes controlling shape. Phenytypic comparisons of mutants both individually and interacting in double mutants will also be made. The other section is concerned with the replication and recombination of T4 DNA. Considerable evidence now indicates that, for ultraviolet-inactivated T4, partial replicas of the parental DNA are replicated in numerous copies, and that recombination among partial replicas from several complementary phages accounts for production of viable phage particles (multiplicity reactivation). We hope to explore this idea by testing whether multiple copies of some genes and no copies of other genes are produced. It is hoped that this approach will allow us to identify the sites at which DNA replication originates. BIBIOGRAPHIC REFERENCES: Simon, L.D., Snover, D., and Doermann, A. H. 1974. Bacterial mutation affecting T4 phage DNA synthesis and tail production. Nature 252:451-455. Kozinski, A. W., and Doermann, A. H. 1975. Repetitive DNA replication of the incomplete genomes of phage T4 petite particles. Proc. Nat. Acad. Sci. (US) 72:1734-1738.